The Castro Valley Adult School Orchestra plays three or four concerts a year, and has done it for more than a decade. What you hear is the result of months of rehearsals and practice. Here's how it works.

Tuesday is the official weekly rehearsal night. As the clock nears 7 p.m., cars begin to arrive at Creekside Middle School. Musicians carry, and sometimes roll, their instruments into the school and down the hall. On the right, the band room door is usually open and folks stream in to their customary places.

With its tall ceiling, lockers and whiteboards, the band room is already set up with chairs and stands. After some rearrangement, instruments come out of their cases and tuning begins. Many of the musicians have been playing in the group for years together, so there is plenty of friendly banter and jokes, including musical, the specialty of a certain clarinetist.

Normally, Director Josh Cohen is already there, sometimes passing out music for new pieces. However, he is training the group to use the Internet to download and print compositions before coming to rehearsal. Programs are planned in advance. It can take time, and often costs money to borrow sheet music that is not available in public domain.

By 7:15 p.m., it's time to start. The oboist plays a piercing "A" and the other musicians match it, bringing the group into tune. Then, with a wave of his slender baton, the orchestra's seasoned leader gets the 30 to 40 musicians under way.

When you attend a concert, you hear the pieces in their entirety, one after the other, but that's not how the orchestra rehearses them. There are frequent stops and lots of repetition to get the sound just right; it takes a couple of months to do it. Sometimes, just the strings will play, and the winds sit and listen, thinking about how their parts fit in. Then, it's their turn to play and the strings listen. Normally, before moving on to another piece - or a movement within it - the group plays the section through from start to finish. Knowing what to play is important, but knowing how it relates to the entire orchestra is essential to a good concert.

As a part of the Castro Valley Adult School, the group meets from September to May, echoing the school year. Hours of practice culminate in public concerts; the next one on Sunday, May 26. Everyone is invited to come by and hear the results. See you there!